Generally, an image reading apparatus, such as a digital copier, for example, can include a scanning module to read a document, a system control unit to temporarily store, edit, transmit, format, and/or convert an image of the document, and a printer unit to form, develop, and fuse the images associated with one or more documents or other image data on a printed medium. With the increase in the number of sheets processed per minute of the digital copier, high speed and high resolution of the scanning module are desirable. For example, when the digital copier is used as a copier, it may be required that the scanning module be more suitable for the high speed, and not high resolution. On the other hand, when the digital copier is used as a scanner, it may be required for the scanning module be more suitable for high resolution, and not high speed. That is, the scanning module of the digital copier may need to satisfy requirements related to both speed and quality, to a lager extend than the requirements that may be needed for a stand-alone scanner.
A step motor can be used to precisely drive and control the scanning module irrespective of, for example, an optical construction and a momentum transmission structure of an optical system. Step motors, however, have poor high speed properties when used to drive the scanning module of a copier requiring high speed operation. Moreover, not only during simple copying having a copy scaling of 100%, but also during enlargement copying or reduction copying having a copy scaling ranging from about 25% to about 400%, the step motor may be required to drive the scanning module at various speeds to read a document. When the scanning module is not properly controlled, vibration and noise can be generated, and an image of the scanned document can be distorted.